Question

The Federal Reserve System publishes data on family income based on its Survey of Consumer Finances. When the head of the household has a college degree, the mean before-tax family income is $85,200. Suppose that 60% of the before-tax family incomes when the head of the household has a college degree are between $75,600 and $94,800 and that these incomes are normally distributed. What is the standard deviation of before-tax family incomes when the head of the household has a college degree?